As multi-connectors used in signal communication requiring impedance matching between boards, there is known one in which transmission lines are given a strip-line configuration by means of four-layer boards (Non-Patent Reference: Hirose Electric Co., Ltd., IT1 Series Product Catalog). In case there are a number of signals requiring impedance matching (below, also called antenna signals or high-frequency signals), this type of connector is used. However, for signals communicating between boards, if e.g. a mobile phone is cited as an example, it is generally the case where the number of high-frequency signals requiring impedance matching is smaller than that of signals for which matching may be ignored. E.g., for antenna signals prior to conversion to the baseband, there is a need to make the characteristic impedances of the transmission paths match accurately. Regarding audio-type signals other than those, or signals like control signals for direct current voltage levels for setting LSI (Large Scale Integration) circuit operating states (including direct current signals, these are below called baseband signals or low-frequency signals), there is no need to take into account the characteristic impedance of the transmission path. Consequently, with respect to all signals, there are many cases where using a multi-connector in which the characteristic impedances are adjusted, such as that described above, is not economical.
Accordingly, for the connection of low-frequency signals for which characteristic impedances may be ignored, common multi-connectors are used and, regarding antenna signals, coaxial connectors are used for which characteristic impedances have been taken into account. Conventional examples thereof are shown in FIGS. 14A and 14B. FIG. 14A is an oblique view showing an example of conventional inter-board connection. On I/O board 131, there are installed a not illustrated antenna as well as a not illustrated speaker, sounder, and vibrating motor. On I/O board 131, there is installed a plug-side multi-connector 132 in parallel with and adjacent to a side thereof. On an extension line of plug-side multi-connector 132, there is installed, in a corner part of I/O board 131, a coaxial receptacle 134.
Plug-side multi-connector 132 on I/O board 131 is mated with a receptacle-side multi-connector 136 installed on an RF (Radio Frequency, below abbreviated as RF)/BB (Baseband, below abbreviated as BB) board 135, in parallel with and adjacent to a side thereof. To coaxial receptacle 134 on I/O board 131, there is fitted a coaxial plug 137 forming one end of a coaxial cable 133, the other end of which is soldered to RF/BB board 135. In this way, for antenna signals requiring matching of characteristic impedances, these have been connected with coaxial cables, whereas for other audio-type signals not requiring characteristic impedance matching, multi-connectors have been used.
In FIG. 14B, there is shown an oblique view showing another conventional example. Elements which are the same as in FIG. 14A are taken to have the same reference numerals and an explanation thereof will be omitted. On I/O board 131 and adjacent to a side thereof, there is installed a first flat cable receptacle 138. First flat cable receptacle 138 is mated with a first flat cable plug 139 forming one end of a flat cable 140 having a plurality of distributing wires, the claddings of which are together united in a single body on the same face. In a corner of I/O board 131 on the longitudinal direction extension line of first flat cable receptacle 138, there is installed a coaxial receptacle 134. Coaxial receptacle 134 is directly connected, without going through a cable, to a coaxial plug 137 directly installed on RF/BB board 135. In first flat cable receptacle 138 on I/O board 131, there is inserted a first flat cable plug 139 forming one end of flat cable 140. To the other end of flat cable 140, there is connected a second flat cable plug 141, second flat cable plug 141 being mated with a second flat cable receptacle 142 installed in parallel with and adjacent to a side of RF/BB board 135. In this way, there is also the method of directly connecting together coaxial connectors installed on a board for antenna signals requiring matching of characteristic impedances and carrying out transmission by using a flat cable for signals not requiring matching of the characteristic impedances.
A multi-connector in which transmission lines are given a strip-line configuration is a connector for which the characteristic impedance Z0 of each transmission line is set to e.g. 50 Ω or 75 Ω, from the relationship shown in the equationZ0=(L/C)1/2.  (1)
L is the inductance per unit length of the transmission line and C is likewise the capacitance per unit length. As is seen from this Eq. 1, in order to adjust the characteristic impedance of each transmission line, there has been the issue of the necessity of having some size for adjustment in each transmission line, resulting in an increase in the size of the whole multi-connector. Such an increased-size multi-connector cannot be used in cellular phone terminals for which miniaturization and the process of making thinner have well advanced. Further, in equipment with few transmission lines requiring matching of characteristic impedances, the result has been the use of matched transmission lines even for signals not requiring matching, something which has been uneconomical.
Accordingly, with the background art, as mentioned, there can be obtained a method of connecting with normal multi-connectors for signals not requiring matching of characteristic impedances and using coaxial connectors for signals requiring matching.
A method can be considered wherein multi-connectors are connected together without using flat cable 140, with the method shown in FIG. 14A, and for coaxial connectors, receptacle 134 and coaxial plug 137 are directly connected without going through coaxial cable 133, with the method shown in FIG. 14B. In the case of directly installing like that a plurality of receptacle components and a plurality of plug components and making them connect all at once, there is the issue that the installation accuracy of each component relative to the others and the finishing accuracy of each component become problems, with the result that the positions of the connection parts do not fit together. If one attempts to make these connect by force, there is the possibility of destroying the connection parts, and even if a connection can be effected, that the reliability or the durability is markedly degraded.
With the objective of preventing this, the method of compensating for the inaccuracy in matching the positions with the other set of connection parts by connecting one set of a plurality of connection parts to cables, is the method shown in FIG. 14A and FIG. 14B. However, whereas it has been possible with this method to prevent the reduction in breakdowns and reliability of the connection parts, but there has been the problem that the number of components ends up increasing. Further, the fact that space is required for the pulling and turning of the cable parts and the fact that man-hours (assembly time) are required for the processing of pulling and turning the cables had become causes for cost increases.